What you will learn
- Decode rwxr-xr-x
- Use chmod and chown safely
- Know when to reach for sudo
New to this? Start here
The basics, in plain English
Every file on a Linux machine has rules about who is allowed to look at it, change it, or run it. These rules are called permissions. They exist so that not everyone can read or break everyone else’s files.
- Permission
- A rule that says what someone is allowed to do with a file.
- Read (r)
- Permission to open and look at the contents of a file.
- Write (w)
- Permission to change or delete a file.
- Execute (x)
- Permission to run a file as a program (only matters for programs and scripts).
- Owner
- The user account that the file belongs to, usually whoever created it.
- Group
- A named set of users who share the same access, like a team.
- chmod
- A command that changes a file’s permissions ("change mode").
- chown
- A command that changes who owns a file ("change owner").
01
The permission triad
Every file has owner, group, and other permissions, each a combination of read (4), write (2), execute (1). 755 means rwx for owner, r-x for everyone else.
02
Changing things
chmod changes the mode, chown changes ownership. Prefer symbolic modes (chmod u+x) when intent matters.
Try it yourself
bash
$chmod 644 config.yml↳Owner can read and write; everyone else can only read.$chmod u+x deploy.sh↳Add execute permission for the owner so the script can run.$chown app:app /srv/app↳Hand ownership of the folder to the app user and group.$ls -l deploy.sh↳Confirm the new permission bits and owner.↳ lines explain what each command does — only the commands get copied
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